1. Field of the Invention
The present invention relates to a self-molding hose which does not require the use of any restricting fabric or other external-pressure molding part and a continuous vulcanization method. More specifically, the present invention relates to (a) a construction of a self-molding hose which may have any of various shapes, and which completely changes the restricting-fabric molding method that has long been in conventional use, (b) a method for the continuous vulcanization of a self-molding hose by means of internal heating, which greatly simplifies the manufacture of such a hose, and (c) a method for the continuous vulcanization of a long, flat rubber hose consisting of a self-molding hose which is thin, light in weight and easy to ship and handle by means of external heating.
2. Prior Art
Except in cases where a special molding method such as the lead encasing system, etc., is used, all conventional hoses are ordinarily formed and vulcanized by the restricting-fabric molding method.
The principal conventional hose shapes may be roughly classified as follows according to structure:
(a) Ply hoses consisting of inner tube rubber, reinforcing fabric layer, and outer skin rubber:
Such ply hoses are formed in an unvulcanized state around a core mold consisting of an iron pipe; the circumference of the hose is formed by wrapping a restricting fabric around the hose, and the hose is then vulcanized in a vulcanizing can.
(b) Braided hoses consisting of inner tube rubber, braided reinforcing layer of stranded yarn (or braided reinforcing layer of wire), and outer skin rubber (exterior surface smooth or with striations):
In most cases, an unvulcanized braided hose is produced without using a core mold, the hose being heated in a vulcanizing can by means of the lead encasing molding system (using internal pressure) Furthermore, such hoses may also be formed and vulcanized by means of a mold forming system using a heating plate. In addition, as in the case of (a) above, such hoses may be produced by forming an unvulcanized braided hose around a core mold, wrapping and tightening a restricting fabric around the outside of the hose, and then vulcanizing the hose by heating the hose in a vulcanizing can.
(c) Wire-containing hoses (single wire or double wire):
Such hoses are available in various types: i.e., the exposed wire type, embedded wire type and semi-embedded wire type, etc. Various configurations (bellows type exterior, smooth exterior, fabric-wrapped exterior, knitted exterior, rubber-wrapped exterior, etc.) are formed in accordance with the conditions of use.
(d) Bandless hoses in which mouthpieces are bonded in an unvulcanized state, and are then vulcanized and fixed by firing.
The hoses described in (a), (c) and (d) above are all formed in an unvulcanized state around a core mold. In all cases, a narrow woven fabric strip is wrapped around the circumference of the resulting unvulcanized hose in two or more layers and is wet with water to produce a tightened state. The hose is thus formed by means of a restricting-fabric system and is then vulcanized by heating in a vulcanizing can.
Particularly in the case of (c) where an external bellows shape is produced, a rope is wrapped and tightened around the circumference of the hose (following the wrapping of the restricting fabric) in order to produce the bellows shape, and the hose is then placed in a vulcanizing can and vulcanized. Furthermore, the mouthpiece areas of the abovementioned bandless hoses (i.e., the areas around the mouthpiece) are pressed especially thoroughly by means of a restricting fabric and a rope. Accordingly, such restricting-fabric molding systems require the troublesome operation of removing the restricting fabric and rope following vulcanization.
As described above, most forming methods and vulcanization methods commonly used in the past have used a laminating system (utilizing a mandrel) for forming and have used direct steam vulcanization in a vulcanizing can. Accordingly, a vulcanizing can which is as long as or longer than the mandrel is required. As a result, the length of hose that can be manufactured is inherently limited, with a length of 10 to 20 m ordinarily being the limit.
Furthermore, direct steam vulcanization suffers from poor thermal efficiency, and when the vulcanizing can is large, time is required in order to elevate the temperature of the vulcanizing can itself. Moreover, in the case of a structure in which various types of soft raw materials are laminated, internal air bubbles are present. Accordingly, the method as follows is ordinarilly used: i.e., the hose is squeezed by means of a restricting fabric so that the hose is degassed. Afterward, the hose is placed in a vulcanizing can and steam-vulcanized; following this vulcanization, the restriction is loosened and the hose is removed from the mandrel. Thus, the manufacturing method includes a large number of intermittent processes.
Such a system is suitable for hoses composed entirely of raw materials in a crude state, thick hoses which require a long vulcanization time, and high-pressure hoses which use a multi-layer reinforcing fabric. Furthermore, methods using a molding system such as lead encasing vulcanization etc., are suitable for small-diameter hoses. In these methods, vulcanization is performed under internal pressure using a mold instead of a restricting fabric; accordingly, the length of hose that can be produced is considerably longer than in the case of the previously mentioned method. However, such methods depend on batch vulcanization of a fixed length of hose. The forming process is quasi-continuous; however, a large and expensive manufacturing apparatus is required for extrusion, braiding, outer skin covering, molding and vulcanizing processes, etc.
Furthermore, conventional methods for the formation and vulcanization of hoses which are flat in cross section include (a) methods in which the hose is formed in a flat cross-sectional shape from the beginning using a flat mandrel, and is vulcanized in this same flat shape, and (b) methods in which the hose is formed in a circular cross-sectional shape using a circular mandrel, after which the mandrel is removed and the unvulcanized circular hose is flattened by pressing and vulcanized by heating.
Furthermore, in the method for manufacturing a flat hose described in Japanese Patent Publication No. 62-49863, substantially the following method is disclosed: "A method for manufacturing a flat hose consisting of (a) a first step in which an unvulcanized cylindrical hose is formed by successively wrapping an inner rubber layer, a fibrous reinforcing layer and a covering rubber layer with some overlap around a mandrel, (b) a second step in which a restricting fabric is wrapped around the circumference of the unvulcanized formed hose, after which the hose is vulcanized by heating, (c) a third step in which the hose is flattened by tightly closing one end thereof and applying vacuum suction to the other end thereof after the restricting fabric and mandrel have been removed, and (d) a fourth step in which the hose is again vulcanized by heating the hose in a flattened state."
In conventional restricting-fabric forming methods as mentioned above, the restricting fabric is generally formed by cutting a woven fabric with a thickness of 0.2 to 0.4 mm to a narrow width. This restricting fabric is then wrapped and tightened around the outer-skin rubber layer of the unvulcanized formed hose. Accordingly, since both edges of the restricting fabric are free edges, the woven texture at the edges of the fabric is disturbed, so that it is difficult to apply uniform force across the entire width of the restricting fabric. Furthermore, since the pressure-maintaining characteristics of such a restricting fabric are poor, the wrapping of at least two or more layers of restricting fabric is required. Moreover, since the restricting fabric bites into the unvulcanized rubber of the the outer skin of the hose, the outer-skin rubber of the hose must be of such a thickness that no problems will arise even if this rubber is bitten into by the restricting fabric, i.e., the thickness of the rubber must be at least two to three times the thickness of the restricting fabric, and the thickness of rubber actually used is generally even 1.5 to 3 mm greater than the required thickness. Accordingly, not only is the external appearance of the hose damaged by the irregular imprinting of restricting-fabric wrapping traces and texture on the outer surface of the hose, but it is also difficult to achieve uniform pressured distribution; hence, dimensional uniformity cannot be obtained.
Furthermore, dirt tends to collect in the imprinted fabric texture of the hose during use, and this dirt is difficult to remove. As a result, the hose becomes unattractively soiled. Moreover, the aforementioned restricting fabric is repeatedly used; however, this restricting fabric becomes soiled during vulcanization in the vulcanizing can, and the degree of soiling increases as the restricting fabric is repeatedly used. Accordingly, from the second occasion of use on, the outer-skin rubber of the hose being manufactured is soiled as a result of the soiling of the restricting fabric. In the case of brightly colored hoses (i.e., hoses with a color other than black), the effect of the coloring is seriously impaired by this soiling. Furthermore, a restricting fabric which is repeatedly used deteriorates as a result of exposure to steam and heat during vulcanization. The strength and elongation of the restricting fabric change as the fabric is repeatedly used, and there is also a change in the uniformity of these properties, so that uniform tightening strength cannot be obtained. Accordingly, bonding strength and dimensions vary from hose to hose.
In addition to the abovementioned defects in terms of physical properties, the restricting-fabric forming method (as described above) requires complicated manufacturing processes, i.e., a restricting fabric preparation process, a restricting fabric and rope wrapping and tightening process, and a restricting fabric and rope removal process, etc. This leads to increased costs. Furthermore, the unvulcanized rubber material in the interior surface layer of the hose has an excessive degree of freedom which leads to various fluctuations. Accordingly, various means of suppressing such fluctuations must be employed.